DEFINITIONS

The following definitions of terms are
made for the purpose of uniform application in the documentation
and preparation of floodplain evaluation reports. Refer
to 23 CFR 650, Section 650.105 for a complete
list of definitions.

Base Flood - The flood or tide having
a one percent (1%) chance of being exceeded
in any given year (100-year flood).

Base Flood Elevation (BFE) -
The water surface elevation of the base flood.

Base Flood Plain - The area subject
to flooding by the base flood.

Design Flood - The peak discharge,
volume if appropriate, stage or wave crest elevation
of the flood associated with the probability of exceedance selected for the design of a highway encroachment. (In other words, the
project will not be inundated at the design flood frequency.)

Designated Floodway - A floodway
designated by a state or local agency. California State
Reclamation Board (Board) definition: A designated floodway
means either: (1) the channel of the stream and that
portion of the adjoining floodplain reasonably required
to provide passage of a base flood or (2) the floodway
between existing levees as adopted by the Board or the
Legislature.

Encroachment - FEMA definition:
Construction, placement of fill, or similar alteration
of topography in the floodplain that reduces the area
available to convey floodwaters. FHWA definition: An
action within the limits of the base floodplain.

Flood Boundary and Floodway Map (FBFM) -
The floodplain management map issued by FEMA that depicts,
on the basis of detailed analyses, the boundaries of
the 100- and 500-year floodplain and the regulatory floodway.

Flood Frequency - The statistical
number of years that takes place before the recurrence
of a flood of the same magnitude. (10-year flood, 50-year
flood, 100-year flood, etc.)

Flood Insurance Rate Map (FIRM) -
The insurance and floodplain management map issued by
FEMA that identifies, on the basis of detailed or approximate
analyses, the areas of 100-year flood hazard in a community.

Flood Insurance Study (FIS) -
It is a report that describes and delineates the Special
Flood Hazard Areas and the elevations of the community.

Floodplain - Any land area subject
to inundation by floodwaters from any source.

Floodplain Evaluation Report -
A technical report which evaluates effects of the floodplain
encroachment concerning the 6 key items identified in
23 CFR 650.111(b)(c)(d) verified by results of the Location
Hydraulic Study, but in greater detail. This report is
required in situations where it is uncertain or clear
that a project may involve a significant encroachment.
This report is to be used as a backup for the Environmental
Assessment/Finding of No Significant Impact (EA/FONSI)
or an Environmental Impact Statement (EIS). The risks,
impacts, and mitigation measures must be summarized in
the National Environmental Policy Act (NEPA) document.

Floodproof - To design and construct
a project to keep floodwaters out or to reduce the effects
of floodwaters.

Floodway - The channel of a river
or other watercourse, plus any adjacent floodplain areas,
which is designated a floodway by a public agency, that
must be kept free of encroachment so that the 100-year
flood discharge can be conveyed without cumulatively
increasing the water-surface elevation more than one
foot above the BFE. (Since the one-foot is already
accounted for, no increase of any amount in the BFE is
allowed in the floodway.)

Floodway fringe - The portion
of the 100-year floodplain that is not within the floodway
and in which development and other forms of encroachment
may be permitted under certain circumstances.

Location Hydraulic Study (same as Figure 804.7A Technical Information for Location Hydraulic Study located in Chapter 800, Topic 804 of the Highway Design Manual) - The
preliminary investigative study to be made of base floodplain
encroachments by a proposed highway action. (This
study must be performed by a registered engineer with
hydraulic expertise.)

Longitudinal Encroachment - An
encroachment that is parallel to the direction of flow. Example:
A highway that runs along the edge of a river is, usually
considered a longitudinal encroachment.

Regulatory floodway - A floodplain
area that is reserved in an open manner by federal, state
or local requirements i.e., unconfined or unobstructed
either horizontally or vertically, to provide for the
discharge of the base flood so that the cumulative increase
in water surface elevation is no more than a designated amount (not to exceed 1 foot as established by FEMA for administering the National Flood Insurance Program).
(Since the 1 foot is already accounted for, no increase
more than 0.00 feet is allowed.)

Risk Analysis - An economic comparison of design alternatives using expected total costs (construction costs plus risk costs) to determine the alternative with the least expected cost to the public. It shall include probable flood-related costs during the service life of the facility for highway operation, maintenance, and repair, for highway-aggravated flood damage to other property, and for additional or interrupted highway travel.

Risk Assessment - An economic
and/or non-economic assessment of the impacts associated
with the floodplain encroachment(s). It is meant to be
more general in detail than a risk analysis. The format
and content of the Summary Floodplain Encroachment Report
form is the minimum required for a risk assessment.

Significant Encroachment - A
highway encroachment and any direct support of likely
base floodplain development that would involve one or
more of the following construction- or flood-related impacts:

A significant potential for interruption or termination
of a transportation facility which is needed for emergency
vehicles or provides a community's only evacuation
route.

A significant risk [to life or property],
or

A significant adverse impact on natural and beneficial
floodplain values.

Special Flood Hazard Areas (SFHAs) -
The areas delineated on an NFIP map as being subject
to inundation by the base (100-year) flood.

Summary Floodplain Encroachment Report (same as Figure 804.7B Floodplain Evaluation Report Summary located in Chapter 800, Topic 804 of the Highway Design Manual) -
It is a floodplain assessment report which addresses
the 6 key items identified in 23 CFR 650.111(b)(c)(d)
verified by results of the Location Hydraulic Study. If
it is determined that a project does not have a significant
encroachment, this form can be used as the documentation
for a Categorical Exclusion (CE) determination. For
federally-funded projects on the State Highway System
(SHS), the Department's Project Engineer will sign the Summary
Floodplain Encroachment Report. For local assistance
projects, this report must be filled out and signed by
the local agency Project Engineer, with concurrence signature
by the District Local Assistance Engineer (DLAE).

INTERAGENCY
COORDINATION

Local, state, and federal water resources
and floodplain management agencies must be consulted
if a proposed action encroaches on a 100-year base floodplain.
Coordination also may occur in order to obtain current
information on development and proposed actions in the
effected watersheds. The Department, or in the case of
local assistance (off SHS) projects, the DLAE, is responsible
for initiating early coordination meetings to discuss
potential floodplain encroachments.

If there are potential impacts to endangered
species or wetlands, and/or if a 404 permit is required,
the federal and state agencies with jurisdiction and
permitting authority should be identified early in the
environmental process. The Department and local agencies are
responsible for early and on-going coordination with
the U.S. Fish and Wildlife Service regarding technical information
and standards for mitigation (as necessary) and with
the U.S. Army Corps of Engineers regarding permit requirements.

The Department evaluates any action which
involves a floodplain encroachment and is responsible
for making the floodplain finding. In the case
of a significant encroachment, FHWA must concur in an "Only
Practical Alternative Finding."

Coordination with FEMA must occur when
floodplain studies indicate that any of the following
four conditions pertain:

A proposed encroachment on a regulatory floodway
(BFE increase) would require an amendment to the floodway
map. (However, it is not likely that any increase
would be allowed by FEMA.)

A proposed encroachment on a floodplain where a detailed
study has been performed but no floodway designated
and the maximum 1 foot increase in the base flood elevation
would be exceeded.

A local community is expected to enter into the regulatory
program within a reasonable period and detailed floodplain
studies are underway.

A local community is participating in the emergency
program and base flood elevation in the vicinity of
insurable buildings is increased by more than 1 foot.

DETERMINING
IF A PROJECT ENCROACHES ON A FLOODPLAIN

The implementation of Executive Order
11988 in transportation projects is addressed by
23 CFR 650 Subpart A entitled "Location and Hydraulic Design
of Encroachment on Floodplains." When SHS
transportation improvements encroach on a base floodplain,
the Department is responsible for the preparation of a Location
Hydraulic Study to assess the risk involved. For
local assistance projects that encroach on a base floodplain,
the local agency is required to prepare a Location
Hydraulic Study. The Location Hydraulic
Study is summarized and appended to the environmental
document for the project. When the Location
Hydraulic Study indicates a significant encroachment
within the base floodplain, as defined by 23 CFR 650.105,
FHWA must approve the encroachment and concur in the
finding that the preferred alternative is the "only
practicable alternative." This information
must be included in the final environmental document/determination. For
further guidance, please see SER
Chapter 38, "NEPA Assignment."

When a local agency's Preliminary Environmental
Study (PES) or the Department's PSR and/or the Preliminary
Environmental Analysis Report (PEAR) indicates that there
are no floodplain impacts, the environmental document
must include this information and the basis for this
conclusion must be documented in the project record.
The determination may be accomplished with an informal
study as long as it provides adequately information to
support the determination.

It should be noted that the absence
of National Flood Insurance Program or State Department
of Water Resources (DWR) base floodplain maps does not
necessarily indicate that there is no base floodplain
in the area. Where no state or federal data is available,
the local agency or the Department is responsible for
examining other data regarding recent flood locations
and developing adequate information and analysis to support
the conclusions presented in the technical report and
the environmental document.

THE LOCATION
HYDRAULIC STUDY

When a floodplain encroachment is anticipated,
the Department or local agency prepares a Location
Hydraulic Study. The Location Hydraulic Study is a preliminary study of
base floodplain encroachments and must be performed by
a registered engineer with hydraulic expertise.

If an increase in the base floodplain
elevation (BFE) is anticipated, a hydraulic computer
model must be run to determine the amount of increase
in order to determine the floodplain encroachment impacts.

The minimum required content of the Location
Hydraulic Study is prescribed in 23 CFR 650 Subpart A, Section
650.111(b)(c)(d) and it must include the following:

(a) National Flood Insurance Program
(NFIP) maps or information developed by the highway agency,
if NFIP maps are not available, are used to determine
whether a highway location alternative will include an
encroachment.

(b) Location studies also must include
evaluation and discussion of the practicability of alternatives
to any longitudinal encroachments.

(c) Location studies must include discussion
of the following items, commensurate with the significance
of the risk or environmental impact, for all alternatives
containing encroachments and for those actions which
would support base floodplain development:

(1)
The risks associated with implementation of the action,

(2)
The impacts on natural and beneficial flood-plain values,

(3)
The support of probable incompatible flood-plain development,

(4)
The measures to minimize flood-plain impacts associated
with the action, and

(5)
The measures to restore and preserve the natural and
beneficial floodplain values impacted by the action.

(d) Location studies must include evaluation
and discussion of the practicability of alternatives
to any significant encroachments or any support of incompatible
floodplain development.

(e) The studies required by Sec. 650.111
(c) and (d) must be summarized in environmental review
documents prepared pursuant to 23 CFR 771.

(f) Local, state, and federal water
resources and floodplain management agencies should be
consulted to determine if the proposed highway action
is consistent with existing watershed and floodplain
management programs and to obtain current information
on development and proposed actions in the affected watershed.

The Location Hydraulic Study provides
the minimum documentation necessary to support a finding
in regard to floodplain encroachment impacts.

MINIMAL
ENCROACHMENT

If the study concludes that there is
no encroachment and/or minimal impact, a Summary
Floodplain Evaluation Report is completed. In
the case of a local assistance project (off the SHS),
this form is filled out and signed by the local agency
Project Engineer, and concurred by the Department's DLAE. In
the case of Department projects on the SHS, the Summary
Floodplain Evaluation Report is signed by the Department's
Project Engineer. This form, and its supporting
study, provide sufficient documentation for a Categorical
Exclusion (CE). The Location Hydraulic Study and
the Floodplain Evaluation Report are
retained in the project file along with any supporting
documentation.

SIGNIFICANT
ENCROACHMENT

When the Location Hydraulic Study concludes
that a proposed action may:

Result in a significant encroachment (as defined
by 23 CFR 650.105) and/or

Is inconsistent with existing watershed and
floodplain management programs, thereby resulting in
incompatible floodplain development, or that

The impacts of the project on the floodplain are
unclear

a Floodplain Evaluation Report is
prepared. This is a self-sufficient technical report,
which is used to support the conclusions of an EA/FONSI
or an EIS. It contains all the information from the Location
Hydraulic Study and is similar to the Summary
Floodplain Encroachment Report but is generally
more detailed. It should include a project description,
a strip map delineating the base floodplain with all
project encroachments identified, and minimization and/or
mitigation measures, as well as a discussion of avoidance
alternatives to each potential encroachment and whether
the alternatives are practicable. The level of detail
in this report will vary depending on the individual
project, but should be commensurate with the complexity
of the project, its risks, and impacts. The risks, impacts
and mitigation measures described in this report form
the basis of discussion in the environmental document. For
further guidance, please see SER
Chapter 38, "NEPA Assignment," Floodplains.

The floodplain “Only Practicable
Alternative Finding” must be included in the final
environmental document. The finding must refer to Executive
Order 11988 and to 23 CFR 650, Subpart A. The finding
must be supported by the following:

The reasons why the proposed action must be located
in the floodplain

The alternatives considered and why they are not
practicable

A statement indicating whether the action conforms
to applicable state or local floodplain protection
standards

For local assistance projects, the DLAE
is responsible for coordinating with FHWA to obtain the “Only
Practicable Alternative Finding”
concurrence for local agency projects.

A copy of the finding must be made available
to the appropriate state and area wide clearinghouse
pursuant to 23 CFR 420. For Department projects this
is the State Office of Planning and Research (OPR), and
for local agency projects, the Office of the County Clerk.

PUBLIC
INVOLVEMENT

Executive Order 11988 requires that
when the only practicable alternative requires encroachment
into a floodplain the public must be given the opportunity
for early review and comment. It also requires that the
risk assessment be filed with the State Clearinghouse.
Existing procedures for public involvement can be used
to meet these requirements. A reference to encroachments
on the base floodplain must be included in public notices
and any encroachments must be identified at public hearings
(Executive Order 11988). See PDPM
Appendix HH for public notice format.

PREPARING
A LOCATION HYDRAULICS STUDY

Location hydraulic studies are performed
to evaluate the base (100 year) flood and the proposed
action's impact(s) on the base floodplain. This study
involves the use of Flood Insurance Study data and NFIP
maps for baseline, and a hydraulic computer model to
determine the new BFE. The items in the Location Hydraulic
Study form below are a suggested minimum for required
documentation:

Location

Name of stream

Bridge number

Geographical reference

Description of proposed action

Hydraulic Data:

Base flood (Q100) Q = ____________
cuffs

Water surface elevation for base flood: ___________________

Flood of record (when available) Q = __________________
cuffs

Flood of record water surface elevation (if available):
____________ feet

Map of Floodplain, with Base Flood (Q100)
and Flood of Record (when available), or the information
developed, if NFIP maps are not available, to determine
whether an alternative will include an encroachment.

Base Flood (Q100) Backwater Potential
Impacts To:

Residences

Other Buildings

Crops

Traffic

Approximate Traffic Volume

Emergency Supply Or Evacuation Route

Emergency Vehicle Access

Practicable Detour Available

School Bus or Mail Route

Approximate Duration of Traffic Interruption for
Base Flood (Q100)

Approximate Value of Base Flood (Q100)
Damages (Required only for the rare situations of moderate
or high risk.)

Roadway:

Property:

Total:

For all alternatives containing encroachments
or which would support base floodplain development, the
following seven items must be evaluated commensurate
with the severity of the risk or environmental impact:

the risk associated with implementation of the action

the impacts on natural and beneficial floodplain
values

the support of probable incompatible floodplain development.

the measures to minimize floodplain impacts associated
with the action

the measures to restore and preserve the natural
and beneficial floodplain values impacted by the action

the practicability of alternatives to any significant
encroachment

the practicability of alternatives to any longitudinal
encroachment.

Local, state, and federal water resources
and floodplain management agencies may need to be consulted
in the preparation of the Location Hydraulics Study to
determine if the proposed action is consistent with existing
watershed and floodplain management programs and to obtain
current information on development and proposed actions
in the affected watersheds.

PREPARER
QUALIFICATIONS

The person performing the hydraulic
study for the Location Hydraulic Study must have
hydrologic and hydraulic engineering expertise and must
be identified in the technical report and in the environmental
document. An environmental specialist should be consulted
regarding social and ecological floodplain impacts.

PREPARING
A SUMMARY FLOODPLAIN ENCROACHMENT REPORT

The Summary Floodplain Encroachment
Report is based on results of the Location Hydraulic
Study and relies on assessment of the key items
stated in 23 CFR 650.111(b)(c)(d), which are reiterated
below. The Summary is completed by the Project
Engineer after consultation with the Hydraulic Engineer
and an environmental specialist. The responses to the
key items can trigger other actions as follows:

1) Is the proposed
action a longitudinal encroachment of the base floodplain?

If the answer is “yes”,
there needs to be an evaluation and discussion of the practical alternatives
to any longitudinal encroachments to supplement
this form.

2) Are the risks
associated with the implementation of the proposed
action significant?

This
answer must be “no” in order to process
this project with a CE.

3) Will the proposed
action support probable incompatible floodplain development?

This
answer must be “no” in order to process
this project with a CE.

4) Are there any
significant impacts on natural and beneficial floodplain
values?

This
answer must be
“no” in order to process this project with
a CE.

5) Routine construction
procedures are required to minimize impacts on the
floodplain. Are there any special mitigation measures
necessary to minimize impacts or restore and preserve
natural and beneficial floodplain values?

If
the answer is “yes”
explain it and supplement this form with the explanation.

6) Does the proposed
action constitute a significant floodplain encroachment
as defined in 23 CFR 650.105q?

This
answer must be “no” in order to process
this project with a CE.

7) Are Location Hydraulic
Studies (same as Figure 804.7A Technical Information for Location Hydraulic Study located in chapter 804 of the Highway Design Manual) that document the above answers on file?

This
answer must be “yes” in order to validate
the answers to the above items.

The Location Hydraulic Study and
the Summary Floodplain Encroachment Report and
their supporting documentation provide the basis for
a CE.

For local assistance projects this form
is to be filled out and signed by the local agency Project
Engineer, and concurred by the Department's DLAE.

PREPARING
A FLOODPLAIN EVALUATION REPORT

The Floodplain Evaluation Report is
prepared when there is a significant encroachment and/or
impact in a base floodplain requiring the preparation of an EA/FONSI or
an EIS.

When an environmental document is to
be prepared for a project which has alternatives that
have permanent features that encroach on a floodplain,
the District Environmental Branch will take the lead
in preparing the Floodplain Evaluation Report.
The technical hydraulic requirements must be evaluated
by the District Hydraulic Engineer. If floodplain encroachments
are significant, then alternatives must be developed
jointly among Design, Hydraulics, and Environmental.

The detail in the report is to be commensurate
with the significance of potential encroachment, and
risk of economic loss, private or public. The report
should include the following:

Project Description, including a strip
map of the project showing the base floodplain and all
project encroachments.

Alternatives to Encroachment. A discussion
of the practicality of alternatives that would avoid
longitudinal or significant encroachments or the support
of incompatible floodplain development.

Risk Assessment. This is prepared by
the District Hydraulic Engineer as part of the location
hydraulic and/or design studies as called for in 23 CFR
650, Subpart A. Risk information is provided for each
individual encroachment throughout the project.

Impacts of the project including the
support of probable incompatible floodplain development
and impacts on natural and beneficial floodplain values.

Measures to minimize floodplain impacts
including measures to restore and preserve floodplain
values affected by the action.

PREPARER
QUALIFICATIONS

The individual performing the Floodplain
Evaluation Report must be a registered professional
engineer or be qualified for registration as a professional
engineer under California law.

The individual determining the natural
and beneficial floodplain values of the floodplain should
be a qualified biologist or wetland ecologist.

INFORMATION
NEEDED FOR PROJECT DELIVERY

Floodplain studies should be undertaken
as early as possible, as the requirement to consider
all practicable alternatives to encroachment upon the
base 100-year floodplain may necessitate a broader study
area or significant modifications in preliminary design
proposals.

The Location Hydraulics Study is
requested simultaneous with other technical reports,
and will determine if further studies are needed.

For local assistance, it is commenced
after completing the PES Form.

For Department projects the Location
Hydraulics Study is undertaken upon receipt
of the request to "Begin Environmental."

Project
Initiation

This information should be included
in the Preliminary Environmental Analysis Report (PEAR)
prepared as part of the Project Initiation Document (PID).

The “Guidelines for the Preparation
of Project Study Reports”
dated November 3, 1999 stipulate that PSR's and project
study report equivalents contain an “inventory
of environmental resources, identification of potential
environmental issues and anticipated environmental processing
type. Potential mitigation requirements and associated
costs should also be identified. “

For projects off the SHS, complete the PES form. The information
required for the PES satisfies the environmental requirement
for the PSR equivalent.

Identification of 100-year base floodplain(s) within
the project area using National Flood Insurance Program
(NFIP) maps.

Identification of any potential floodplain encroachments
by the proposed project and construction activities.

Regional Transportation
Plan

This information should be documented
in the Environmental Impact Report (EIR) prepared for
the RTP and serve as a
building block in subsequent decision-making.

An RTP requires the preparation of a California Environmental Quality Act
(CEQA) environmental document, normally a program or master
EIR. The Department encourages the MPO/RTPA's to include the
following information, as appropriate, in the environmental
document for the plan:

Identification of floodplains within the transportation
corridor or sub area using National Flood Insurance
Program (NFIP) maps available online at FEMA's Flood Mapping Hazard page.

Draft
Project Report

This information should be presented
in the draft environmental document or used as supporting
documentation for a Categorical Exemption/Categorical Exclusion, as appropriate:

Verification of all information from RTP stage & PID
stage and:

Identification of floodplain encroachments and potential
project impacts to base floodplain in a Location
Hydraulics Study and Floodplain Evaluation Report.

Project
Report

This information should be presented
in the final environmental document.

“Floodplain Only Practicable Alternative Finding” if
appropriate.

Cost estimates for mitigation measures, as defined,
for the Mitigation Cost Tracking System

ACTIVITIES
THAT MAY OCCUR DURING THE PROJECT DESIGN PHASE

After the environmental process is completed,
detailed design studies of the encroachment are required
as a part of the final design process. If the design
selected involves a significant encroachment, it must
be supported by analysis of design alternatives with
consideration given to capital costs, risks, and to other
economic, engineering, social, and environmental concerns.
The detail of the studies shall be commensurate with
the risk associated with the encroachment and with other
economic, engineering, social, and environmental concerns.
The required contents of the design studies are specified
in 23 CFR 650.117.

ACTIVITIES
THAT MAY OCCUR DURING THE RIGHT-OF-WAY PHASE OR
DURING CONSTRUCTION

Following the approval of an environmental
document and prior to proceeding to request major approvals
or grants for the project phase, the Department must determine
if the environmental document remains valid. Any
major changes in floodplain incursion or effects from
the project at these phases may initiate a reevaluation. For
more information, refer to the SER, Vol. 1, Chapter 33, "Reevaluations."

MAP REVISION

It is implied in the Federal-Aid Policy Guide (non-regulatory
supplement for 23 CFR 650A) that a map revision is only
required when a project results in any increase in the
BFE in a floodway or increases the BFE by more 1 foot
in a base floodplain. This contradicts the FEMA requirement
to submit a map revision for any increases in the BFE
in a base floodplain. In order to be consistent with
the NFIP, it is advisable to consult with the California Department of Water Resources (DWR) and/or
FEMA to determine if a map revision is necessary for
increases less than 1 foot.

The map revision is a very complex process.
Hence, it is highly recommended that DWR and/or FEMA
be contacted for technical assistance for this process.
A basic outline of the information that needed is listed
below:

Pre-project survey of existing cross-sections of
the stream or watercourse at the proposed project site.

Design must meet local, state, and FEMA criteria
and all other permit requirements.

Original FIS models (HEC-2, HEC-RAS or WSPRO, etc.)
must be rerun with new data to reflect the new base
floodplain boundaries.

Map revision data must be submitted
to FEMA within 6 months of project completion. However,
the coordination/consultation for the revisions should
begin during the design phase of a project.

It is not likely that any increases
of elevation in the regulatory floodway will be allowed
by any of the regulatory agencies.

ADDITIONAL DEFINITIONS

Freeboard - A factor of safety
usually expressed in feet above a flood level for purposes
of flood plain management. "Freeboard" tends
to compensate for the many unknown factors that could
contribute to flood heights greater than the height calculated
for a flood frequency and floodway conditions, such as
wave action, and floating debris under bridge openings. Definition from 23 CFR 650: The vertical clearance of the lowest structural member of the bridge superstructure above the water surface elevation of the overtopping flood.

National Flood Insurance Program
(NFIP) - The federal program that enables property
owners to purchase flood insurance.

Overtopping flood - The flood
frequency at which a flow to occurs over the highway,
over the watershed divide, or through structure(s) provided
for emergency relief. Definition from 23 CFR 650: The flood described by the probability of exceedance and water surface elevation at which flow occurs over the highway, over the watershed divide, or through structure(s) provided for emergency relief.

Practicable - Capable of being
done within reasonable natural, social, or economic constraints.

Preserve - To avoid modification
to the functions of the natural floodplain environment
or to maintain it as closely as practicable in its natural
state.

Restore - To reestablish a setting
or environment in which the functions of the natural
and beneficial floodplain values adversely impacted by
the highway agency action can again operate.

Riverine Area - A river-like
area.

Transverse Encroachment - An
encroachment that is perpendicular to the direction of
flow. (Example: A bridge encroachment on the
floodplain is normally considered to be transverse encroachment.